Learning Objective Describe the types of lymph vessels and lymph trunks and their roles. Key Points The lymph trunks drain into the lymph ducts, which in turn return lymph to the blood by emptying into the respective subclavian veins. There are two lymph ducts in the body: the right lymph duct and the thoracic duct. There are four pairs of lymph trunks: jugular lymph trunks, subclavian lymph trunks, bronchomediastinal lymph trunks, and lumbar lymph trunks.
In addition, the intestinal lymph trunk is unpaired. The intestinal lymph trunk and the thoracic lymph duct contain chyle, a mixture of emulsified fats from the intestines and lymph fluid.
Full Text After filtration by the lymph nodes , efferent lymphatic vessels take lymph to the end of the lymphatic system. Lymphatic Trunks A lymphatic trunk is any large lymph vessel that forms from the convergence of many efferent lymph vessels. There are four sets of of lymph trunks that are paired with a right and left half, and one unpaired trunk: Jugular lymph trunks, located in the neck, drain lymph fluid from the cervical lymph nodes of the neck.
Subclavian lymph trunks, located beneath the clavicle, drain lymph fluid from the apical lymph nodes around the armpit, which carry lymph from the arms. Blood vessels also have valves, but only in low pressure venous circulation. They function similarly to lymphatic valves, though are comparatively more dependent on skeletal muscle contractions. The lymphatic system comprises a network of conduits called lymphatic vessels that carry lymph unidirectionally towards the heart.
Describe the structure of the lymphatic system and its role in the immune system and blood circulation. The lymphatic system is a circulatory system for lymphatic fluid, comprising a network of conduits called lymphatic vessels that carry the fluid in one direction toward the heart.
Its functions include providing sites for certain immune system functions and facilitating plasma circulation in the cardiovascular system. The lymphatic system is composed of many different types of lymph vessels over a wide distribution throughout the body. Lymphatic System : The lymph nodes and lymph vessels in human beings. Lymphatic vessels are most densely distributed near lymph nodes: bundles of lymphoid tissue that filter the lymph fluid of pathogens and abnormal molecules.
Adaptive immune responses usually develop within lymphatic vessels. Large lymphatic vessels can be broadly characterized into two categories based on lymph node distribution. Lymph nodes are most densely distributed around the pharynx and neck, chest, armpits, groin, and around the intestines.
Afferent and efferent lymph vessels are also most concentrated in these areas so they can filter lymph fluid close to the end of the lymphatic system, where fluid is returned into the cardiovascular system. Conversely, lymph nodes are not found in the areas of the upper central nervous system, where tissue drains into cerebrospinal fluid instead of lymph, though there are some lymph vessels in the meninges.
There are few lymph nodes at the ends of the limbs. The efferent lymph vessels in the left and lower side of the body drain into the left subclavian vein through the thoracic duct, while the efferent lymph vessels of the right side of the body drain into the right subclavian vein through the right lymphatic duct.
The lymphatic vessels start with the collection of lymph fluid from the interstitial fluid. This fluid is mainly water from plasma that leaks into the intersitial space in the tissues due to pressure forces exerted by capillaries hydrostatic pressure or through osmotic forces from proteins osmotic pressure. When the pressure for interstitial fluid in the interstitial space becomes large enough it leaks into lymph capillaries, which are the site for lymph fluid collection. In comparison to cardiovascular capillaries, lymphatic capillaries are larger, distributed throughout connective tissues, and have a dead end that completely prevents backflow of lymph.
That means the lymphatic system is an open system with linear flow, while the cardiovascular system is a closed system with true circular flow. Lymph flows in one direction toward the heart.
Lymph vessels become larger, with better developed smooth muscle and valves to keep lymph moving forward despite the low pressure and adventia to support the lymph vessels. As the lymph vessels become larger, their function changes from collecting fluid from the tissues to propelling fluid forward.
Lymph nodes found closer to the heart filter lymph fluid before it is returned to venous circulation through one of the two lymph ducts.
Lymph circulates to the lymph node via afferent lymphatic vessels and drains into the lymph node in the subcapsular sinus. Lymph transport refers to the transport of lymph fluid from the interstitial space inside the tissues of the body, through the lymph nodes, and into lymph ducts that return the fluid to venous circulation. Lymphatic capillaries are the site of lymph fluid collection from the tissues.
The fluid accumulates in the interstitial space inside tissues after leaking out through the cardiovascular capillaries. The fluid enters the lymphatic capillaries by leaking through the minivalves located in the junctions of the endothelium.
Under ordinary conditions these minivalves prevent the lymph from flowing back into the tissues. In addition to interstitial fluid, pathogens, proteins, and tumor cells may also leak into the lymph capillaries and be transported through lymph.
The lymph capillaries feed into larger lymph vessels. The lymph vessels that receive lymph fluid from many capillaries are called collecting vessels. Semilunar valves work together with smooth muscle contractions and skeletal muscle pressure to slowly push the lymph fluid forward while the valves prevent backflow.
The collecting vessels typically transport lymph fluid either into lymph nodes or lymph trunks. Lymph circulates to the lymph node via afferent lymphatic vessels. The lymph fluid drains into the node just beneath the capsule of the node into its various sinus spaces. These spaces are loosely separated by walls, so lymph fluid flows around them throughout the lymph node.
The sinus space is filled with macrophages that engulf foreign particles and pathogens and filter the lymph. The sinuses converge at the hilum of the node, where lymph then leaves the node via an efferent lymphatic vessel toward either a more central lymph node or a lymph duct for drainage into one of the subclavian veins.
The lymph nodes contain a large number of B and T lymphocytes, which are transported throughout the node during many components of the adaptive immune response.
When a lymphocyte is presented with an antigen such as by an activated helper T cell , B cells become activated and migrate to the germinal centers of the node, where they proliferate and differentiate to be specific to that antigen. When antibody-producing B cells are formed, they migrate to the medullary central cords of the node. They resemble blood capillaries, but are much more porous to surrounding fluids due to the following two features:.
Valvelike openings form at the juncture of adjacent endothelial cells. Unlike the tightly joined endothelial cells that make up the walls of blood capillaries, those of lymph capillaries loosely overlap. When fluid pressure increases in surrounding regions, the overlapped cells separate, allowing fluids to enter the lymph capillary. When pressure inside the capillary exceeds the pressure outside, the spaces between the endothelial cells close, holding fluids inside the capillary.
Anchoring filaments attach the endothelial cells of the lymphatic vessels to surrounding collagen. When interstitial fluid pressure increases, the anchoring filaments prevent the endothelial cells from collapsing, keeping the spaces between the endothelial cells open. CDC on Lymph trunk. Books on Lymph trunk.
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